The present invention is of a method for detecting the spalling of a layer of alkali and/or metal buildup material from the surface of a refractory lining in a metallurgical furnace, and particularly to monitoring the rate of change of the temperature of said refractory lining at a plurality of spaced locations in order to detect spalling of said layer.
In the production of metal from ore in a blast furnace, for example in an iron blast furnace, a layer of deposits is formed on the interior surface of the refractory walls of the furnace shaft. The layer may consist of alkali and/or metal material. Once formed, the deposited layer tends to keep growing during operation of the furnace. Occasionally portions of the layer break away from the refractory wall and descend with the charge materials to the molten iron bath contained in the furnace hearth. The spalled off portions of the layer are commonly referred to as a scab. When the scab reaches the molten iron and dissolves, a significant loss of temperature occurs. The unexpected decrease in iron temperature causes significant changes in the distribution of chemical components such as silicon and sulfur between the molten slag and iron. Increases in sulfur content may necessitate scrapping a substantial amount of the iron produced.
U.S. Pat. No. 4,412,090 to Kawate etal, discloses a thermal sensor for detecting the temperature distribution in a deposit layer on the refractory walls of a blast furnace. The sensor provides data to be used for the development of a method to suppress the formation and growth of the deposit layer during operation of the blast furnace.
U.S. Pat. No. 4,358,953, discloses a temperature probe construction that is used in the thermal sensor of the patent to Kawate et al described above.
U.S. Pat. No. 5,961,214 to Groth et al, of common assignee with the present application, discloses a method for determining the thickness of a protective layer of solidified metal skull formed on the refractory hearth of a blast furnace. The refractory hearth has temperature probes embedded in the floor and walls of the hearth. The method includes periodically measuring temperatures indicated by the probes and determining the campaign maximum and current average temperature readings to locate two solidification isotherms representing the wear line of the refractory and the inner surface of the protective metal layer. The thickness of the protective layer is determined from the distance between the solidification isotherms.
None of the references teach or suggest a method for the detection of the spalling of significant portions of the layer of buildup on the refractory walls of a blast furnace shaft.
The present invention is of a method for detecting the spalling of a layer, for example a layer of alkali and/or metal, deposited on the interior surface of a refractory lining of a metallurgical furnace. The invention is particularly applicable to blast furnaces, especially blast furnaces for producing iron. The method includes monitoring the temperature of the refractory lining at a plurality of spaced locations as a function of time, calculating a rate of change of the temperature at each said location, establishing a first threshold level of the rate of change of temperature of said refractory lining indicative of spalling of a portion of a layer of buildup from said lining, and determining when the rate of change of temperature of said refractory of at least one of said locations exceeds said first threshold level. Preferably the method includes determining when the rate of change of temperature at a predetermined number of adjacent locations exceeds said first threshold level. This indicates that a significant portion of the layer has spalled off. Desirably a plurality of ranges of the rate of change of temperature is established as a function of time indicative of a plurality of conditions of spalling of the layer of buildup.
In a most preferred form the method further comprises providing additional heat to a bath of molten metal contained in a hearth at a lower end of the furnace when a significant portion of the layer of buildup has spalled. More preferably the additional heat provided is based upon either the number of adjacent locations at which the rate of change of temperature either exceeds said first threshold level or the number of adjacent locations within ranges indicative of spalling of the layer of buildup.